Optical disk with grooves and pits of different depths

ABSTRACT

An optical disk for use in an optical memory device having guide grooves and pits on one surface thereof, wherein the depth of the guide grooves is different from that of the pits and the distance from the bottom face of each of the guide grooves to the other surface of the optical disk opposite to the one surface of the optical disk on which the guide grooves and pits are disposed is the same as the distance from the bottom face of each of the pits to the other surface of the optical disk opposite to the one surface of the optical disk on which the guide grooves and pits are disposed, and a method for the production of optical memory master plates that are used for the production of the above-mentioned optical disk.

This application is a divisional of application Ser. No. 08/032,540,filed on Mar. 17, 1993, now U.S. Pat. No. 5,399,461, which is acontinuation of Ser. No. 07/679,997 filed on Apr. 1, 1991, nowabandoned, which is a continuation of Ser. No. 07/233,540, filed on Aug.18, 1988, now abandoned the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical disk for use in optical memorydevices that conduct a recording operation, a regenerating operation, oran erasing operation of information using laser beams, and to a methodfor the production of the optical disk.

2. Description of the Prior Art

In recent years, optical memory devices have become recognized as adense and mass memory device. Optical memory devices can be classifiedinto three groups consisting of regenerative memory devices, write oncememory devices and rewritable memory devices. Optical memory devices,which can be classified as write once memory devices and rewritablememory devices, generally have guide tracks on a disk made of glass orplastics so as to guide a light beam for recording and/or regeneratinginformation to a given portion of the optical memory device. A portionof each of the guide tracks is formed into a pit-shape, resulting in atrack address by which the position of the guide track can beidentified. When the sectionalization of each guide track is needed toadminister information, sector addresses are also disposed in the disk.

FIG. 10 shows a conventional disk 500 with guide tracks that areconstituted by grooves 100. Information such as track addresses, sectoraddresses or the like disposed on the disk 500 in advance are formedinto the shape of pits 200. In general, on a disk with guide grooves andpits, a recording medium is formed by the vacuum evaporation method, thesputtering method, the spin-coating method or the like. When necessary,a protective substrate and/or a resin film is laminated on the recordingmedium, resulting in an optical memory device.

Because information is recorded on the guide tracks 100 (FIG. 10) usinglight such as laser beams or the like, the shape of the grooves 100significantly influences the tracking servo signal characteristicsessential to keeping a light beam spot on a given guide track. To obtaingood tracking servo signal characteristics, the depth of guide groovesformed in the disk are usually set to be around λ/8 n (wherein λ is awavelength of light and n is the refractive index of the disk). Incontrast, because information such as track addresses, sector addressesor the like are formed into a pit-shape on the disk and read off byutilizing a diffraction effect of light in the pits, the depth of eachpit is set to be around λ/4 n. In this way, the depth of guide grooves100 of a disk 500 for use in optical memory devices is different fromthe depth of the pits 200 of the said disk. This kind of disk 500 isdesigned such that, as shown in FIG. 10, one surface 300 of the disk 500is flush with the surface of the land 400 positioned between theadjacent guide grooves 100 that are formed on the said surface 300 ofthe disk 500.

FIGS. 11a to 11d show a process for producing the above-mentioned disk500. As shown in FIG. 11a, a resist film 600, formed on a disk plate 10is illuminated with a laser beam 700, resulting in guide grooves and pitlatent images on the resist film 600. The intensity of illumination oflaser beam 700 for formation of guide groove latent images is set lowerthan that of the formation of pit latent images. Then, the resist film600 is developed, as shown in FIG. 11b, resulting in a pattern 660corresponding to the guide grooves 100 and pits 200 shown in FIG. 10,the depths of which are different from each other. The disk plate 10with a pattern 660 is then subjected to a dry or wet etching treatment,resulting in a disk 500 such as that of FIG. 10. Alternatively, as shownin FIG. 11c, a metal film 800 made of nickel (Ni) or the like is formedon the disk plate 10 with a pattern 660 by the sputtering method, thevacuum evaporation method and/or the electroforming method, resulting ina stamper (i.e., a master plate) 880 as shown in FIG. 11d. By the use ofthe stamper 880, a plastic disk with a structure such as that shown inFIG. 10 can be formed by an injection technique.

The shape of the bottom of each of the grooves 100 formed on a disk 500is a transcription of the shape of the top surface of the patternedphotoresist film 660. Thus the bottom face of each of the grooves of thedisk 500 mirrors the unevenness of the top surface of the patternedresist film 660. This unevenness causes noise when information writteninto the guide grooves (i.e., guide tracks) 100 of the disk 500 using alaser beam is regenerated by a laser beam producing inferiorregenerated-signals.

SUMMARY OF THE INVENTION

The optical disk of this invention, overcomes the above-discussed andnumerous other disadvantages and deficiencies of the prior art, byhaving guide grooves and pits on one surface thereof, wherein the depthof the guide grooves is different from that of the pits and the distancefrom the bottom face of each of said guide grooves to the other surfaceof said optical disk opposite to said one surface of said optical diskon which said guide grooves and pits are disposed is the same as thedistance from the bottom face of each of said pits to the other surfaceof said optical disk opposite to said one surface of said optical diskon which said guide grooves and pits are disposed.

The method for the production of optical memory master plates of thisinvention comprises forming a photoresist film on a disk plate, exposingsaid photoresist film to beams, developing said photoresist filmresulting in a patterned photoresist film, and forming a metal film onsaid disk plate with the patterned photoresist film, wherein in saidexposure process, a plurality of beams that are disposed in the radiusdirection of said disk plate illuminate said photoresist film through anobject lens, then said plurality of beams are shifted radially in such away that an area that is exposed after said beams are shifted issuperposed on a part of the area that has been exposed before said beamsare shifted, and then said beams illuminate said photoresist film,resulting in an exposed area that is wider than the exposed area formedbefore said beams are shifted, said widely exposed area constituting aguide-groove latent image.

In a preferred embodiment, the disk plate is made of glass or plastics.The above-mentioned optical disk is produced by the use of the masterplate.

The method for the production of optical memory master plates of thisinvention comprises forming a photoresist film on a disk plate, exposingsaid photoresist film to beams, developing said photoresist filmresulting in a patterned photoresist film, and forming a metal film onsaid disk plate with the patterned photoresist film, wherein in saidexposure process, a first beam and a second beam illuminate saidphotoresist film with a fixed gap therebetween in the radius directionof said disk plate so as to form a first exposed area and a secondexposed area, then these beams are shifted radially with said fixed gaptherebetween in such a way that said first beam is superposed with apart of said second exposed area, then said first and second beamsilluminate said photoresist film, and then the above-mentioned steps arerepeated, resulting in unexposed areas with a width that corresponds tosaid fixed gap and widely exposed areas that are composed of said firstand second exposed areas.

In a preferred embodiment, the disk plate is made of glass or plastics.The above-mentioned optical disk is produced by the use of the masterplate.

Thus, the invention described herein makes possible the objectives of(1) providing an optical disk for use in optical memory devices, inwhich the bottom face of each of the guide grooves is so flat and smooththat optical memory devices that produce high quality regeneratedsignals can be obtained; and (2) providing a method for producing theoptical disk by which the guide grooves can be formed with accuracy bymeans of laser beams that are at a relatively low intensity level.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood and its numerousobjects and advantages more apparent to those skilled in the art byreference to the accompanying drawings which are given by way ofillustration only, and thus are not limitative of the present invention,and wherein

FIG. 1 is a perspective view showing an enlarged portion of an opticaldisk of the present invention for use in an optical memory device;

FIGS. 2a to 2d are schematic diagrams illustrating a production processfor making the optical disk of FIG. 1.

FIG. 3 is a diagram showing an optical system used in the productionprocess shown in FIGS. 2a to 2d;

FIG. 4 is a schematic diagram showing an exposing process for productionof an optical memory master plate used for the production of an opticaldisk according to present invention.

FIGS. 5a-5b and 6a-6b are schematic diagrams showing the steps forformation of guide groove latent images on photoresist film in theexposing process shown in FIG. 4;

FIGS. 7a and 7b are schematic diagrams showing the steps for formationof pit latent images on a photoresist film in the exposing process shownin FIG. 4;

FIG. 8 is a schematic diagram showing the disposition of pits andgrooves on a photoresist film corresponding to the header of the masterplate according to the method of the present invention.

FIG. 9 is the time charts of the modulating signals and the deflectingsignals of laser beams by which the pit latent images and the guidegroove latent images corresponding to the pits and the grooves of FIG. 8are formed on the photoresist film;

FIG. 10 is a perspective view showing a conventional disk;

FIGS. 11a to 11d are schematic diagrams showing a production process ofthe disk shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an optical disk having pits and guidegrooves in which the bottom face of each pit is flush with the bottomface of each guide groove.

EXAMPLE 1

FIG. 1 shows an optical disk according to the present invention, whichis made of glass, plastics or the like. The optical disk 5 has guidegrooves 1, which function as guide tracks, and pits 2 on one surface 51thereof. Both the bottom face of each groove 1 and the bottom face ofeach pit 2 are positioned at the same distance from the other surface 52of the optical disk 5; that is, the bottom face of each of the grooves 1is flush with that of each of the pits 2. The depth D1 of each of thegrooves 1 is different from the depth D2 of each of the pits 2. Thevalue of D1 is set to be approximately λ/8 n and the value of D2 is setto be usually in the range from approximately λ/8 n to λ/4 n (wherein λis a wavelength of light and n is the refractive index of the opticaldisk).

FIGS. 2a to 2d show a production process for the optical disk shown inFIG. 1. On a disk plate 10 of glass or plastics, as shown in FIG. 2a, aphotoresist film 6 is formed, which is then illuminated with light 7such as laser beams or the like via an optical lens 20 so as to formlatent patterns corresponding to the desired shape of guide grooves 1and pits 2 shown in FIG. 1. Then, the photoresist film 6 with a latentpattern is developed, as shown in FIG. 2b, resulting in a pattern 66that corresponds to the guide grooves 1 and the pits 2 shown in FIG. 1.

The production of such a pattern 66 is described in detail below. FIG. 3shows an optical system with a laser apparatus 11 used in theabove-discussed process for the production of pattern 66. The opticalsystem includes a laser apparatus 11, beam splitters 12 and 18,reflectors 13 and 19, optical modulators 14 and 15, a deflector 16, andan 1/2 wavelength plate 17. A laser beam emitted from the laserapparatus 11 is split into two laser beams 21 and 22 by the beamsplitter 12. The laser beam 21 arrives at the beam splitter 18 throughthe optical modulator 14 and the deflector 16. The other laser beam 22is reflected by the reflector 13 and arrives at the reflector 19 throughthe optical modulator 15 and the 1/2 wavelength plate 17. The laser beam22 is reflected by the reflector 19 and arrives at the beam splitter 18.The laser beams 21 and 22 meet in the beam splitter 18 and are incidenttogether upon an object lens 20. The 1/2 wavelength plate 17 functionsto change the wave surface of the laser beam 22, thereby preventing thelaser beams 22 from interfering with the laser beam 21.

FIG. 4 shows the exposure of a photoresist film 6 to the laser beams 21and 22 at the times of the production of an optical memory master plate.

FIGS. 5a-5b and 6a-6b show the steps for formation of guide groovelatent images on the photoresist film in the exposing process shown inFIG. 4. The laser beams 21 and 22 condensed into a spot fashion,respectively, by the object lens 20 illuminate the top surface of thephotoresist film 6 in such a way that the laser beam spots arepositioned at a fixed distance d therebetween in the radius direction ofthe disk plate 10 (FIGS. 5a and 5b). The unexposed area 23 that ispositioned between the beams 21 and 22 constitutes an area correspondingto a land 4 of FIG. 1 after it is developed. The exposed areas 24 and 25that are exposed to the beams 21 and 22 constitute areas correspondingto guide grooves 1 of FIG. 1 after they are developed. Then, the opticalsystem is shifted in the radius direction of the disk plate 10 (i.e., inthe direction of arrow A) so that the light spot of the laser beam 22can be superposed on a part of the above-mentioned exposed area 24 by adistance L. Then, the disk plate 10 is rotated, so that as shown inFIGS. 6a and 6b, an exposed area 1 that is composed of theabove-mentioned exposed area 24 and an newly exposed area 25a, both ofwhich overlap by the area 250 with a width L, is formed and at the sametime, an exposed area 24a is newly formed across an unexposed area 23awith a distance d from the said exposed area 1.

The above-mentioned steps are repeated, and the exposed areas 1 that arewider than the exposed area 24 or 25 are formed on the photoresist film6. The width d of the unexposed areas 23 and 23a has no relation withthe shifting pitch of the optical system and can be adjusted by changesin the gap between the laser beams 21 and 22, so as to be maintainedprecisely.

FIGS. 7a and 7b show the step for the formation of pit latent images onthe photoresist film corresponding to the header of the optical memorymaster plate. FIG. 8 shows the disposition of pits and guide grooves onthe photoresist film corresponding to the header of the master plate.FIG. 9 shows time charts of modulating signals and deflecting signals ofthe laser beams 21 and 22 by which the exposed areas of FIG. 8 areformed.

The modulating signals S1 and S2 (FIG. 9) of the laser beams 21 and 22,respectively, are output and the exposed areas 24 and 25 are formed onthe photoresist film 6. At a time of t1, the modulating signals S1 andS2 of the laser beams 21 and 22 are off and the deflecting signal S3 ofthe laser beam 21 is on (FIG. 9), so that as shown in FIG. 7a, the laserbeam 21 is deflected toward the position 21a and the incidence of thelaser beams 21 and 22 upon the object lens 20 is cut off. Then, duringthe time periods T1, T2 and T3 the modulating signal S1 of the laserbeam 21 is output (FIG. 9) and the laser beam 21a illuminates thephotoresist film 6, resulting in exposed areas 24a with a narrow widthon the header of the master plate. The output power of the laser beam21a is slightly lowered, which makes the spot diameter small, and at thesame time, the spread of the laser beam 21a is deflected by thedeflector 16 that receives the deflecting signal S3 in such a way thatthe spot of the laser beam 21a is positioned at a line extending fromthe center of the above-mentioned exposed area 1 (FIG. 7b), andaccordingly the laser beam 21a is incident upon the object lens 20.Then, at a time t2, the deflecting signal S3 of the laser beam 21 is offand the modulating signals S1 and S2 of the laser beams 21 and 22,respectively, are on, so that the laser beams 21 and 22 are againincident upon the object lens 20, resulting in exposed areas 24 and 25on the photoresist film 6. The width d of each of the above-mentionedunexposed areas can be precisely adjusted by the deflection of the laserbeam 21 by means of the deflector 16 or by the rotation of the reflector19 by means of a reflector-rotating means (not shown).

The heights of the unexposed areas 23 and 23a of a pattern 66 that isobtained by the development of the photoresist film 6 depend upon theintensity of the laser beams 21 and 22, and the time length of thedevelopment or the like. The depth and width of the pits can be set at adesired value by controlling the intensity of the laser beam 21a (FIGS.7a and 7b) at the times of formation of pits. In this way, the desiredpattern 66 corresponding to the guide grooves 1 and the pits 2 of theoptical disk 5 of FIG. 1 is formed on the resist film 6.

Then, on the disk plate 10 with the pattern 6 (FIG. 2b), as shown inFIG. 2c, a metal film 8 made of nickel (Ni) or the like is formed by thesputtering method, the vacuum evaporation method, the electroformingmethod, or the like, resulting in a stamper (i.e., a master plate) 88shown in FIG. 2d. By the use of the stamper 88, an optical disk 5 suchas that shown in FIG. 1 can be produced by an injection technique, acasting technique or the like. The bottom faces of the grooves 1 and thepits 2 of this optical disk 5 are very flat and smooth because theytranscribe the surface of the glass or plastic disk plate 10 that isvery flat and smooth.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

What is claimed is:
 1. An optical disk for use in optical memory devicecapable of recording and reproducing information by irradiation of alight beam, the disk comprising:a disk plate having a first surface anda second surface; an array of pits, arranged on a first top portion ofthe first surface, for storing information regarding the disk, each ofthe pits having a first depth which is defined by a bottom surface ofeach pit and the first top portion; and a plurality of guide grooves,formed on a second top portion of the first surface, for guiding thelight beam so as to attain a guide tracking, each of the guide grooveshaving a second depth which is defined by a bottom surface of each guidegroove and the second top portion; wherein the first top portion isspaced a greater distance from the second surface than the second topportion, and the bottom surfaces of the pits and the guide grooves areequidistant from the second surface, thereby the first depth beinggreater than the second depth.
 2. An optical disk according to claim 1,wherein the first depth is approximately λ/4n and the second depth isapproximately λ/8n.
 3. An optical disk according to claim 1, wherein thesecond top portion defines lands formed between the guide grooves.
 4. Anoptical disk according to claim 1, wherein the difference in spacing ofthe first and second top portions defines a step on the first surface.5. An optical disk according to claim 1, wherein the informationregarding the disk stored by the plurality of pits includes trackaddresses for identifying a position of each of the guide grooves.
 6. Anoptical disk according to claim 1, wherein the information is recordedon the guide grooves.